Solutions for Progress 

Water-Effect Ratio Studies

RBI conducted the first water-effect ratio (WER) study for a Central Valley discharger in 2005, which was a copper WER study for the El Dorado Irrigation District’s (EID's) Deer Creek Wastewater Treatment Plant. As part of this effort, RBI informed the Central Valley Regional Water Quality Control Board  (Regional Water Board) NPDES permitting staff on how the U.S. EPA pre-authorized the use of WERs in the California Toxics Rule for application in the NPDES permitting process. To complete the study, RBI prepared a study plan that was approved by the Regional Water Board, coordinated with bioassay and analytical laboratories, calculated the discharger-specific copper WERs, and prepared the final WER study report. This first WER study report was peer reviewed by U.S. EPA, which confirmed that the study approach was consistent with applicable U.S. EPA guidance and the conclusions were supported by the data. The discharger-specific WER derived from the study successfully resolved the copper compliance issue at the Deer Creek Wastewater Treatment Plant. Since then, RBI has successfully resolved copper compliance issues for the following additional POTWs through completing WER studies that derived discharger-specific WERs:

  • EID’s El Dorado Hills Wastewater Treatment Plant,
  • Town of Windsor
  • City of Colfax
  • City of Galt

In addition, RBI has directed preliminary WER testing that evaluated potential aluminum and zinc WERs for other wastewater dischargers. RBI is the industry leader in conducting WER studies for POTWs.